Electro-pilotstatic valve for gas burners

ABSTRACT

The object of the present invention is hence an electro-actuator ( 1 ) for gas cooktops or the like, piloted by actuating means, comprising at least one safety electromagnet ( 4 ) forming part of a pilotstat, at least one cut-off means ( 2 ) of the fuel gas, substantially a sleeve provided with an outlet channel ( 22 ) and a conduit ( 23 ) of the fuel gas, of at least one safety shutter ( 20 ) whereon a pushing/pulling force (F F ) acts that operates the safety closing of said outlet channel ( 22 ), at least a service shutter ( 20 ), and a support structure ( 10 ) provided with a cavity ( 100 ) within which a stem ( 21 ) is placed sliding, whereto at least one ferromagnetic element ( 32 ) cooperating with said safety electromagnet ( 4 ) and said shutter ( 20 ) cooperating with the cut-off means ( 2 ) of the fuel gas are constrained, where said safety shutter ( 20 ) and said service shutter ( 20 ) coincide in a same shutter ( 20 ); said ferromagnetic element ( 32 ) being anchored to said safety electromagnet ( 4 ) through an anchoring force (F P ) of mutual attraction that arises when said safety electromagnet ( 4 ) is electrically powered, in particular through the flame sensor of pilotstat, 
     characterised in that:
 
said pressing/pulling force (F F ) is of magnetic nature and susceptible to be won by the command forces (F S ) exerted for the opening of said outlet channel ( 22 ) and by said anchoring force (F P ).

The present invention relates to an electro-pilotstatic system for gasburners, in particular an electro-actuator for gas cooktops or the likeequipped with a safety system.

Currently the prior art provides different solutions for the deliveryand regulation of the fuel gas for cooktops and also contemplatesdifferent systems that ensure safety.

For example, the common cooktops are equipped with a safety system,advantageously comprising valves, which automatically stops the flow ofthe fuel gas to the burner in case of accidental switching off of theflame.

The most known and used solution provides the use of a linear shut-offvalve mounted in series to a manual regulation valve, typically a rotaryplug valve (tap).

The user, by interacting with the tap, performs a manual action thatmoves back the shutter of the safety valve, bringing a ferromagnetickeeper constrained thereto in contact with an electromagnet allowing thepassage of gas for the ignition of the burner; said electromagnet beingcontrolled and supplied by a flame detector.

Said flame detector generally makes use of a thermocouple placed in theproximity of the flame of the burner; in the presence of a flame saidthermocouple generates a potential difference capable of producing anelectric current that feeds the solenoid of said electromagnet.

The magnetic field created by the solenoid is sufficient to retain theshutter in its open position and to ensure the supply of the fuel gas tothe burner.

In the event that the flame accidentally goes out, the thermocouple doesno longer produce any potential difference, as a consequence it ceasesthe electrical supply to the solenoid of the electromagnet, which is nolonger able to generate a magnetic field sufficient to retain theshutter, which under the thrust of an elastic means, such as a spring,returns to the rest position closing the valve and thus interrupting thegas flow; this avoids that in case of inadvertent switching off of theflame the gas continues to be delivered by the valve, dispersing in thesurrounding indoor environment (normally kitchens or rooms for thepreparation and cooking of foods and meals) with serious risks forpeople and things.

The electromagnet—thermocouple coupling is known as “pilotstat” and iswidely used on each burner to ensure a safe use of the cooktops.

The various solutions proposed by the prior art provide to keep separateand distinct the devices adapted to the control and regulation of thegas flow from the devices adapted to safety.

Said division involves the installation of multiple components incooktops or the like where the nature of the overall dimensions isextremely relevant and space saving is one of the objectives to bepursued for the designers and manufacturers.

Normally closed shut-off valves exist on the market, which carry out thepassage of gas through a remote electrical control.

In fact, said shut-off valves are closed in the rest position, as amatter of safety, while in the working position they are constantly keptopen through a continuous control signal.

This operating configuration involves a waste of energy and heating ofthe electrical and electronic equipment; the latter may generate overtime a degradation of the insulator of the electric cables and adeterioration of the same circuit, leading to malfunctions or breakages.

The main object of the present invention is to provide anelectro-actuator for gas cooktops or the like that combines in a singleelement both the part concerning safety and the part concerning theregulation of the flow.

In particular, the main object of the present invention is to provide anelectro-actuator for gas cooktops or the like which integrates in asingle element the regulation of the flow of the fuel gas and theautomatic cut-off of the same in case of accidental switching off of theflame.

A further object of the present invention is to provide anelectro-actuator for gas cooktops or the like which allows to feed thecontrol and regulation devices of the gas flow only during theactuations of the same, by suspending the electrical supply once theregulation is complete.

This and other objects, which shall appear clear hereinafter, areachieved with an electro-actuator for gas cooktops or the likeillustrated in the following description and in the annexed claims,which constitute an integral part of the same description.

Further features of the present invention shall be better highlighted bythe following description of a preferred embodiment, in accordance withthe patent claims and illustrated, purely by way of a non-limitingexample, in the annexed drawing tables, in which:

FIG. 1 shows a section view of the electro-actuator according to a firstembodiment of the present invention in the closed or rest position;

FIG. 2 shows a section view of the electro-actuator according to thesame first embodiment of the present invention in the open or workposition;

FIG. 3 shows a section view of a second embodiment of theelectro-actuator according to the present invention in the closed orrest position;

FIG. 4 shows a section view of a second embodiment of theelectro-actuator according to the present invention in the open or workposition;

FIG. 5 shows a section view of a further executive variant of theelectro-actuator according to the present invention;

FIG. 6 shows the electro-actuator according to the present inventionprovided with a membrane;

FIG. 7 compares two section views of the electro-actuator according tothe present invention shown in the open condition and in the closedcondition;

FIG. 8 shows a summary table of the parameters and operatingconfigurations of the electro-actuator according to the presentinvention;

FIGS. 9a and 9b show two examples of gas valves suitable for blownburners wherein the electro-actuator according to the invention could beused.

Unless otherwise specified, in this report any possible spatialreference such as the terms up/down, front/rear, right/left etc. refersto the position in which the elements are represented in the annexedfigures.

The features of the invention are now described using the references inthe figures.

In relation to the figures, the electro-actuator 1 for gas cooktops orthe like according to the present invention, is provided with a safetyelectromagnet 4, shut-off means 2 of the fuel gas, substantially asleeve equipped with an outlet channel 22 and a fuel gas duct 23, atleast one service shutter 20 and at least one safety shutter 20,cooperating with said shut-off means 2, whereon a pressing/pulling forceacts that operates the safety closing of said electro-actuator 1,advantageously said pressing/pulling force being of magnetic or elasticnature.

Said service shutter and said safety shutter coincide in a same shutter20 that performs two tasks simultaneously:

-   -   the cut-off of the fuel gas to be sent to the burner;    -   the safety closing of the shut-off means 2 of the fuel gas when        the burner or the flame are switched off.

Said pressing/pulling force acts on said shutter 20 operating the safetyclosing of said electro-actuator 1, in particular said pressing forceoperates the safety closing of said outlet channel 22 of the fuel gas.

The electro-actuator 1 comprises a support structure 10, ofsubstantially tubular shape and preferably made of non-magneticmaterial, at the ends whereof a safety electromagnet means 4 and acut-off means 2 of the fuel gas, substantially a sleeve, arerespectively arranged.

Inside the said support structure 10 a cavity 100 is provided withinwhich a stem 21 provided with an element 30 sensitive to the magneticfield is placed sliding.

The stem 21, suitably controlled, operates the opening and/or closing ofthe shut-off means 2 of the fuel gas.

A detailed description of the figures, brought by way of a non-limitingexample is provided below.

FIG. 1 shows a section of the electro-actuator 1 according to thepresent invention in the closed or rest position.

Inside the said support structure 10 a cavity 100 housing a bottom 101is provided, within which a cursor 30 integral with a stem 21 is placed,said cursor 30 being sensitive to the magnetic field.

Said bottom 101 cooperates with the cursor 30 to achieve the magneticforce that operates the safety closing of the electro-actuator 1according to the present invention.

In this construction variant said cursor 30 comprises a permanentmagnet, while said bottom 101 comprises a ferro-magnet.

Nothing prevents, in accordance with alternative embodiments, that saidcursor 30 may advantageously comprise a ferro-magnet, while the bottom101 may comprise a permanent magnet, without altering the correctoperation of the electro-actuator 1, or that both may comprise permanentmagnets.

In general, the magnetic interaction between the bottom 101 and thecursor 30, due to the materials with which they are made and to theirreciprocal position, must ensure for any condition of use and for anyposition of the shutter 20 or the electromagnet 4, the “normally closed”condition.

The position of the cursor 30 and the bottom 101, the materials withwhich they are created and the switching on and/or off modes of theburner, are thus parameters to be chosen and defined in order to ensurethe “normally closed” condition of the electro-actuator 1.

Said bottom 101, comprising a disk of ferromagnetic material, isprovided with a central hole 111 for the passage and the sliding of thestem 21, said stem 21 being integral with said cursor 30.

One end of said stem 21, advantageously made of non-magnetic material,is provided with at least one ferromagnetic element 32 that cooperateswith the safety electromagnet means 4; the other end of the stem 21 isintegral with the shutter 20.

The shutter 20 cooperates with the sleeve 2 of the fuel gas; inparticular said shutter 20 opens or closes the outlet channel 22 of thefuel gas, allowing the passage of the fuel gas from the conduit 23 tosaid outlet channel 22, towards the corresponding burner (not shown).

The safety electromagnet 4 is advantageously controlled through thethermocouple placed in the proximity of the flame zone of the burner,according to what shown and described above with reference to the priorart.

When the burner is switched off, therefore, the thermocouple does notprovide any type of electric current to said electromagnet 4, which isthen de-energized and does not produce any magnetic field; in this casethere is not any kind of significant interaction between theelectromagnet 4 and the ferromagnetic element 32.

In FIG. 1, the electro-actuator 1 is in the closed position and theshutter 20 closes the outlet channel 22 of the fuel gas.

The closing of the electro-actuator 1 according to this variant of theinvention is guaranteed by the magnetic force existing between thecursor 30 and the bottom 101; said magnetic force keeps the stem 21fixed and stable, so as to lock the shutter 20 at the mouth of theoutlet channel 22 of the fuel gas, preventing the entry to the fuel gas.

By analysing in more detail the closed configuration represented in FIG.1 it can be deduced that the only active force is that magnetic betweenthe bottom 101 and the cursor 30.

In fact, the electromagnet 4 is de-energized, so there are notsignificant attractive magnetic forces between said electromagnet 4 andthe ferromagnetic element 32; the stem 21, therefore, is translatedtoward the sleeve 2 by the attractive magnetic force between the bottom101 and the cursor 30.

Said magnetic force achieves and ensures the closing of theelectro-actuator 1, engaging the shutter 2 at the mouth of the outletchannel 22 of the fuel gas, so as to occlude it.

FIG. 2 shows a section view of the electro-actuator according to thepresent invention in the open or work position.

In the figure the electro-actuator 1 is visible in the open position,i.e. with the outlet channel 22 of the fuel gas communicating with theconduit 23 of the fuel gas.

Considering FIG. 1 and FIG. 2 let us assume that the switching on of theburner of the cooktop is desired.

The user, by means of suitable actuating means (not shown), manuallyactivates the electro-actuator 1, by translating the stem 21 towardssaid electromagnet 4, bringing the ferromagnetic element 32 in contactwith said electromagnet 4.

The shutter 20, being positioned on the stem 21, is moved away from saidoutlet channel 22 of the fuel gas 22, thus allowing the gas to enterfrom the outlet channel 22 and reach the burner, allowing the switchingon thereof.

When the flame of the burner is switched on, the thermocouple starts togenerate an electric current that energizes the electromagnet 4,ensuring the magnetic coupling between said electromagnet 4 and theferromagnetic element 32.

In fact, the attractive magnetic force between the electromagnet 4 andthe ferromagnetic element 32 is greater than the attractive magneticforce present between the cursor 30 and the bottom 101; this allows tokeep the electromagnet 4 and the ferromagnetic element 32 integral.

With the flame switched on the mechanical action (exerted by the userthrough the actuating means) that kept the electromagnet 4 and theferromagnetic element 32 in contact is suspended, and the opening of thevalve is ensured by the thermocouple, which generates the electriccurrent necessary to keep the electromagnet 4 energized.

In the transitional period that goes from the switching on commandimparted by the user and the entry into operation of the thermocouple,the passage of the gas is ensured by said mechanical action thatmaintains the ferromagnetic element 32 in contact with the electromagnet4.

In case of accidental switching off of the flame, the thermocouple doesnot generate any potential difference, as a consequence theelectromagnet 4 is no longer fed electrically and the magnetic couplingwith the ferromagnetic element 32 of the stem 21 is lost; this resultsin the closing of the electro-actuator 1 due to the magnetic force ofattraction between the bottom 101 and the cursor 30.

If wished to proceed with the voluntary switching off of the burner, theuser, through suitable actuating means, uncouples the ferromagneticelement 32 from the electromagnet 4, or stops the passage of electriccurrent to the electromagnet; also in this case the closing of theelectro-actuator 1 is given by the attractive force between the cursor30 and the bottom 101.

The closing command may further be obtained by means of a microswitch onthe thermocouple circuit or through a by-pass circuit of theelectromagnet 4, through which when the user closes, all or part of theelectric current generated by said thermocouple passes, making themagnetic field of the electromagnet 4 so small as to allow the pressingforce to close the passage of the fuel gas.

The embodiment shown in FIG. 1 and FIG. 2 described above, provides tokeep the valve in the closed position through a magnetic force generatedby at least one ferromagnetic element and at least one permanent magnet.

In the case just described, an attractive force that brings the cursor30 towards the bottom 101 is employed, bringing the stem 21 to translatetowards the sleeve 2 and engage the shutter 2 at the mouth of the outletchannel 22 of the fuel gas occluding it.

A construction variant (not shown) provides to employ a repulsive force.

Said configuration (valve closed in the rest condition) remains suchuntil the user manipulates the electro-actuator 1 through the actuatingmeans to switch on the burner of the cooktop.

In the existing electro-actuators, an elastic force is used, normallyexerted by a compression helical spring in order to achieve the“normally closed” condition.

The electro-actuator 1 according to the embodiment just described, ischaracterised in that it achieves the “normally closed” conditionthrough a magnetic force and uses it to ensure the closing of the outletchannel 22 of the fuel gas when said electric actuator 1 is closed or inrest condition.

The replacement of the spring with a magnetic force implies severaladvantages, first of all the elimination of an element subject to wear.

In fact, the spring is a component subject to constant mechanicalstress, resulting in deterioration and wear of the elastic element thatmay lead to operating problems.

Furthermore, the spring may jam or stop compromising the safety of thevalve, while the magnetic force existing between a ferro-magnet and apermanent magnet, by its nature, does not present issues of this kind.

With ref. to FIGS. 3 and 4 a second possible embodiment of the presentinvention is now described, illustrated by way of a non-limitingexample. FIG. 3 shows a section of the electro-actuator 1 according tothe present invention in the closed or rest position.

In this construction variant the electro-actuator 1 in addition to theelements already described, advantageously comprises a solenoid 33connected to the walls of the said support structure 10 through thesupport element 330.

Said solenoid 33 is coaxial with respect to the support structure 10 andcooperates with the cursor 30 to achieve the closing and opening of theelectro-actuator 1.

In FIG. 3, the electro-actuator 1 is in the closed position and theshutter 20 closes the outlet channel 22 of the fuel gas, as previouslydescribed (i.e., through a magnetic force).

FIG. 4 shows a section view of the electro-actuator according to thepresent invention in the open or work position, that is with the outletchannel 22 of the fuel gas communicating with the conduit 23 of the fuelgas.

Considering FIG. 3 and FIG. 4 let us assume that the switching on of theburner of the cooktop is desired.

The user, by means of suitable actuating means (not shown), activatesthe electrical supply to the solenoid 33, which immediately creates amagnetic field inside the support element 330.

Said induced magnetic field exerts a force on the cursor 30 forcing thestem 21 to translate towards the electromagnet 4, the force generated bysaid induced magnetic field being greater and of opposite direction withrespect to the attractive magnetic force existing between the bottom 101and the cursor 30.

The translation of the stem 21 brings the ferromagnetic element 32 incontact with the surface of the electromagnet 4 and opens the outletchannel 22 of the fuel gas.

The electrical supply to the solenoid 33, which no longer generates anytype of magnetic field, is suspended when the flame is switched on, andthe keeping of the valve open is ensured by the attractive magneticforce between the ferromagnetic element 32 and the electromagnet 4.

In the transitional period that goes from the switching on commandimparted by the user and the entry into operation of the thermocouple,the gas passage is ensured by the solenoid 33, which continues to be fedelectrically for said time interval, so as to maintain, through theinteraction between the induced magnetic field and the cursor 30, theferromagnetic element 32 in contact with the electromagnet 4.

In case of accidental switching off of the flame, the electromagnet 4 isno longer fed electrically by the thermocouple and the magnetic couplingwith the ferromagnetic element 32 is lost; the closing of theelectro-actuator 1 is carried out by the magnetic force of attractionbetween the bottom 101 and the cursor 30.

If wished to proceed with the voluntary switching off of the burner, theuser, through suitable actuating means, activates the electrical supplyto the solenoid 33, but with reversed polarity compared to the switchingon signal, so as to generate a magnetic field in the opposite directionto the previous, or interrupting the passage of electric current in theelectromagnet 4.

In this case the magnetic field induces the cursor 30 to move toward thesleeve 2, by uncoupling the ferromagnetic element 32 from theelectromagnet 4, and locking the shutter 20 at the mouth of the outletchannel 22 of the fuel gas, through said magnetic force.

Said configuration, that is of closed valve in rest condition, remainssuch until the user manipulates the electro-actuator 1 through theactuating means to switch on the burner of the cooktop.

The electro-actuator 1 according to the present invention provides forpowering the solenoid 33 only during the switching on and voluntaryswitching off step of the burner, while as regards the normal activityof the burner the solenoid 33 is de-energized.

Said solution allows to reduce the energy absorption of theelectro-actuator 1 according to the present invention and protects fromexcessive heating of the electrical parts due to the long operatingtimes.

Preferably the typical operating voltage for the solenoid 33 issubstantially less than or equal to 24V in direct current and the numberof solenoid coils is substantially greater than or equal to 200.

In order to further reduce heating of the solenoid 33 and to increaseits operational life, it can be advantageously fed with a square wavewith variable duty cycle so as to obtain the maximum movement force.

The duty cycle, or useful work cycle is the fraction of time that anentity passes in an active state in proportion to the total timeexamined, for example considering a square-wave signal the duty cycle isthe ratio between the duration of the active signal and the total periodof the signal, and serves to express how much portion of period thesignal is active for.

Furthermore, the electro-actuator 1 according to the present inventionallows the switching on and switching off of the burner from remotelocations, because the actuating commands carried out by the user areessentially of the electrical and non-mechanical type.

FIG. 5 shows a section view of a further possible executive variant ofthe electro-actuator according to the present invention.

In FIG. 5 the electro-actuator 1 is in the closed position and theshutter 20 closes the outlet channel 22 of the fuel gas.

In this construction variant, the pressing force is of elastic natureand the electro-actuator 1 is maintained in its normally closed positionby an elastic loading means, advantageously a compression helical spring200.

In fact, by observing the figure it is understood that the spring 200insists on the shutter 20 while keeping the outlet channel 22 of thefuel gas closed.

Compared to previous embodiments, the magnetic force (that keeps theoutlet channel of the fuel gas closed) has been replaced with an elasticforce given by said spring 200.

In this construction variant a cursor 210 is provided comprising aferromagnetic element.

Said cursor 210 cooperates with the bottom 102, also made offerromagnetic material, placed inside the cavity 100.

With respect to what previously described, let us assume that theswitching on of the burner of the cooktop is desired.

The user, by means of suitable actuating means (not shown), activatesthe electrical supply to the solenoid 33, generating a magnetic fieldthat induces the cursor 210 to translate towards the electromagnet 4,the force generated by said induced magnetic field being greater and ofopposite direction with respect to the elastic force that thecompression helical spring 200 exerts on the shutter 20.

The shutter 20 is moved away from said outlet channel 22 of the fuelgas, thus allowing the gas to enter from the outlet channel 22 and reachthe burner.

The translation of the stem 21 brings the ferromagnetic element 32 incontact with the surface of the electromagnet 4.

When the ferromagnetic element 32 and the electromagnet 4 are in contactand said electromagnet 4 is powered by the thermocouple (or flamesensor) exposed to the flame, it is intuitive that the magnetic forceexisting between said ferromagnetic element 32 of the stem 21 and saidelectromagnet 4 is greater than the elastic force generated by thecompression helical spring 200.

The closing command is obtained substantially with the annulment of theelectric current generated by the thermocouple.

Alternatively the variant of FIG. 5 may provide the use of the cursor210 only, eliminating the bottom 102, provided that said cursor 210 ismade of magnetic material so as to be able to be controlled by thesolenoid 33.

In short, the electro-actuator 1 according to the present inventioncomprises at least a pressing/pulling force that achieves the normallyclosed condition, interrupting the passage of the fuel gas to theburner.

Said pressing/pulling force may advantageously be of elastic or magneticnature, according to the construction variants.

Where the pressing/pulling force is of elastic nature, theelectro-actuator 1 comprises at least an elastic means, such as forexample a compression spring, while in the case of pressing/pullingforce said electro-actuator comprises at least one ferromagnetic elementand at least one permanent magnet, suitably arranged and cooperatingwith each other.

In general said pressing/pulling force is susceptible to be won by thecommand forces exerted for the opening of said outlet channel 22 andfrom said anchoring force between the ferromagnetic element 32 and theelectromagnet 4.

With regards to the opening and closing command of the electro-actuator1 according to the present invention, it can be advantageously manual orelectrically controlled.

In the case of manual opening and closing the user, through appropriatecontrol means, translates the stem 21 of the valve bringing theferromagnetic element 32 in contact with the electromagnet 32, while inthe case of closing the user uncouples said elements.

The opening and closing by electric control takes place through theinteraction between a cursor, sensitive to the magnetic field, and anelectromagnet, advantageously a solenoid 33.

If said cursor comprises a permanent magnet the opening and closingcommand may be exerted through said solenoid 33, in particular throughthe inversion of its poles.

In the case in which said cursor comprises a ferromagnetic element, theopening of the electro-actuator 1 takes place via the solenoid 33 thatpushes said cursor towards the bottom 102, while the closing command maybe obtained substantially causing the annulment of the electric currentgenerated by the thermocouple.

This can be obtained at least in two ways:

-   -   through a single normally closed switch on the thermocouple        circuit, which the user opens to cut-off the current, provided        that the cooktop is equipped with a suitable certified        electronics;    -   through a by-pass circuit of the coil of the normally open        electromagnet that the user closes diverting on it substantially        all the current passing in the coil significantly reducing the        magnetic field thereof.

Nothing prevents to apply these switching off modes also to the variantin which the cursor is a permanent magnet.

FIG. 6 shows the electro-actuator 1 according to the present inventionprovided with an interference membrane 230 placed in proximity of thestem 21 inside the conduit 23 of the fuel gas, in order to prevent theinflow of said fuel gas inside the same electro-actuator.

Advantageously said interference membrane 230 is applicable to all theexecutive variants described.

FIG. 7 compares two section views of the electro-actuator according tothe present invention shown in the open condition and in the closedcondition.

In figure the numerals of the various components are not provided inorder to facilitate the reading and understanding, and advantageouslythe terms and the concept expressed by FIG. 7 extend to all theembodiments previously illustrated and described.

Referring then to the numerals of FIGS. 1, 2, 3, 4, 5 and 6, a legend ofthe terms of FIG. 7 is provided below, where:

-   -   D is the outer diameter of the valve body (or the maximum        dimension thereof if of a non-cylindrical section);    -   X is the instant position of the reference (e.g., the        barycentre) of the element 30, 210 with respect to a reference        integral with the body of the valve (e.g., the bottom 101) that        varies between a minimum value Xmin, in correspondence of which        said outlet channel 22 is closed, and a maximum value Xmax, in        correspondence of which said outlet channel 22 is open;    -   C is the maximum stroke of the translating elements 20, 21, 30,        32, 210, between them constrained, and being C=Xmax−Xmin;    -   F_(F) is the force of mutual attraction between the element 30        and the bottom 101, variable as a function of the instant        position X, and such that F_(F)=F_(F) _(_) _(MAX) when X=Xmin;        F_(F)=F_(F) _(_) _(min) when X=Xmax, where obviously F_(F) _(_)        _(MAX) is the maximum attraction force, while for F_(F) _(_)        _(min) is the minimum attraction force;    -   the command force Fs is the resultant on the element 30 along        the direction “x” of the forces generated by the solenoid 33,        that is said command force Fs is the resultant of the forces        generated by the solenoid 33 acting on said cursor 30, the        direction and intensity whereof depend on the sign and intensity        of the current circulating through the coils of the solenoid;    -   the anchoring force FP is the force of mutual attraction between        the element 32 and the electromagnet 4, which arises when the        flame is lit and thermocouple active; variable as a function of        the instant position X.

Said force F_(F) is the pressing/pulling force that operates the safetyclosing of said electro-actuator 1, and is susceptible to be won by thecommand forces F_(S) exerted for the opening of said outlet channel 22and by said anchoring force F_(P). Additionally the anchoring forceF_(P) is such that:

-   -   F_(P)=0 when the flame is switched off (electromagnet 4 not        powered);    -   F_(P)≠0 when the flame is switched on (electromagnet 4 powered)        and is worth: F_(P)=F_(P) _(_) _(MAX) when X=XMAX, FP=F_(P) _(_)        _(min) when X=Xmin, where obviously F_(P) _(_) _(MAX) is the        maximum anchoring force, while for F_(P) _(_) _(min) is the        minimum anchoring force. In a preferred embodiment the        electro-actuator according to the present invention is        characterised by the simultaneous existence of all the following        conditions (where the modules of the forces must be considered):    -   D≤20 [mm];    -   0.08 D<C<0.4 D;    -   F_(P) _(_) _(MAX)>F_(F) _(_) _(min);    -   F_(F) _(_) _(MAX)>F_(P) _(_) _(min);    -   F_(S) _(_) _(MAX(+))>F_(F) _(_) _(MAX);    -   (F_(S) _(_) _(MAX(−))+F_(F) _(_) _(mm))>F_(P) _(_) _(MAX).

In particular, once the geometry is fixed the intensity and direction ofthe current being equal F_(S) may be considered approximately constantas the position X varies and equal to F_(S) _(_) _(MAX(+)) when theresultant of the forces on the element 30 acts in the positive directionof the axis x (opening command of the outlet channel 22); F_(S) _(_)_(MAX(−)) when said resultant acts in the negative direction of the sameaxis (closing command of the outlet channel 22).

Additionally F_(S) may take a positive value FS_MAX(+) and a negativevalue F_(S) _(_) _(MAX(−)) corresponding to the sign of the electriccurrent that feeds the solenoid 33.

FIG. 8 shows a summary table of the parameters and possible operatingconfigurations of the electro-actuator according to the presentinvention.

The table shows:

-   -   State: indicates the state of the electro-actuator 1 and fuel        gas burner that is:        -   “rest”: the electro-actuator 1 is in a normally closed            position and the burner is switched off;        -   “transitional”: the electro-actuator is switching from the            closed position to the open position or vice versa and the            burner may be switched on if the switching on is commanded            or switched off if the switching off is commanded;        -   “switched on”: the electro-actuator 1 is in the open            position and the burner is switched on;        -   “switched off”: the electro-actuator 1 is in the normally            closed position and the burner is switched off.    -   Flame: indicates the presence of the flame to the fuel gas        burner (ON the flame is present; OFF the flame is absent).    -   Solenoid: indicates the electrical supply to the solenoid, being        ON(+) a positive electrical supply and ON(−) a negative        electrical supply of the solenoid 33.

Preferably the command ON(+) provides for the opening of theelectro-actuator 1, while the command ON(−) provides for the closing ofthe said electro-actuator 1.

The state is explained for various operating conditions of the burnercontrolled by the electro-actuator 1 according to the present inventionwhere:

-   -   “normal switching on” indicates the switching on of the said        burner and the opening of the electro-actuator 1;    -   “voluntary switching off” indicates the switching off of the        said burner and the closing of the said electro-actuator 1;    -   “accidental switching off” indicates the switching off of the        said burner and the closing of the said electro-actuator 1;    -   “attempted switching on” indicates the failed switching on        attempt of said burner and the closing of the said        electro-actuator 1.

In short the active forces in the electro-actuator 1 may be summarisedas follows:

-   -   valve closed: only F_(F) is present that carries out the        normally closed;    -   valve open: both F_(F) and F_(P) are present, where F_(P) keeps        the valve open being F_(P)>F_(F);    -   F_(F), F_(P) and F_(S) are present in the transitional.

It is clear that the combination in various ways of the variants justdescribed may lead to further variants without departing from the scopeof the invention as well as many embodiments and applications arepossible.

The electro-actuator according to the invention may for example be veryuseful for the supply of the premix burners for cooktops, both of theatmospheric type and blown type such as those described in documentsAN2014A000130, AN2014A000176, AN2015A000041, AN2015A00042,AN2015A000060, AN2015A000061 and 102015000018411.

By “premix burner” it is meant a burner in which the primary air is fedin amounts sufficient for the complete combustion without the need forthe supply of secondary air on the flames.

By “blown burner” it is meant a burner in which the primary air intendedto take part in the combustion is not drawn by Venturi effect but is fedinto the same burner through a fan and in precisely controlled amounts.In such burners the primary air therefore enters through calibratedorifices and in many cases it is appropriate that it is fed into orintercepted simultaneously upon the feeding/interception of the gas.

FIGS. 9a and 9b show two examples of gas valves 25 suitable for blownburners and wherein the electro-actuator according to the invention,which is not shown in details, may be used.

Both figures with 21 indicate the stem whereto one or more shutters 20are constrained that intercept the passage of gas and air from therespective distribution conduits 23 and 24 towards the outlet channel 22to the burner.

In particular, FIG. 9a shows two valves 25 in each of which acorresponding single shutter 20 intercepts two concentric air and gasorifices while in FIG. 9b the stem 21 carries two shutters 20 dedicatedthe one to the interception of the gas and the other of the air.

1. Electro-actuator (1) for gas cooktops or the like, piloted byactuating means, comprising at least one safety electromagnet (4)forming part of a pilotstat, at least one cut-off means (2) of the fuelgas, substantially a sleeve provided with an outlet channel (22) and aconduit (23) of the fuel gas, of at least one safety shutter (20),cooperating with said cut-off means (2) of the fuel gas, whereon a force(FF) acts that operates the safety closing of said outlet channel (22),at least a service shutter (20), where said safety shutter (20) and saidservice shutter (20) coincide in a same shutter (20), and a supportstructure (10) provided with a cavity (100) within which a stem (21) isplaced sliding, where one end of said stem (21) is provided with atleast one ferromagnetic element (32) that cooperates with said safetyelectromagnet means (4), while the other end of the stem (21) isintegral with said shutter (20); said ferromagnetic element (32) beinganchored to said safety electromagnet (4) through an anchoring force(FP) of mutual attraction that arises when said safety electromagnet (4)is electrically powered, in particular through the flame sensor ofpilotstat, I. characterised in that: said force (FF), that operates thesafety closing of said outlet channel (22), is of magnetic nature andsusceptible to be won by a command force (FS) exerted for the opening ofsaid outlet channel (22) and by said anchoring force (FP); wherein saidforce (FF), that operates the safety closing of said outlet channel(22), is given by the magnetic mutual attraction between a cursor (30)placed on said stem (21) and a bottom (101) placed in said cavity (100);wherein said force (FF), that operates the safety closing of said outletchannel (22), achieves and ensures the closing of the electro-actuator(1), engaging the shutter (20) at the mouth of the outlet channel (22)of the fuel gas, so as to occlude it.
 2. Electro-actuator (1) accordingto claim 1, wherein the instant position (X) of said cursor (30) inrelation to said bottom (101) varies between a minimum value (Xmin), incorrespondence of which said outlet channel (22) is closed, and amaximum value (Xmax), in correspondence of which said outlet channel(22) is open, characterised in that: the force of mutual attraction (FF)between said cursor (30) and said bottom (101) is variable as a functionof the instant position (X), and such that said force is maximum(FF=FF_MAX) when the instant position is minimum (X=Xmin); while thisforce is minimum (FF=FF_min) when the instant position is maximum(X=Xmax); the anchoring force (FP) between the ferromagnetic element(32) and the electromagnet (4) is variable as a function of the instantposition (X), and such that said force is maximum (FP=FP MAX) when theinstant position is maximum (X=Xmax), while the said force is minimum(FP=FP_min) when the instant position is minimum (X=Xmin); II. andcharacterised in that: said maximum anchoring force (FP=FP_MAX) isgreater than the minimum mutual attraction force (FF=FF_min) betweensaid cursor (30) and said bottom (101); said maximum mutual attractionforce (FF=FF MAX) between said cursor (30) and said bottom (101) isgreater than said minimum anchoring force (FP=FP_min). 3.Electro-actuator (1) according to claim 1, wherein said bottom (101)comprises a ferromagnetic element and said cursor (30) comprises apermanent magnet.
 4. Electro-actuator (1) according to claim 1, whereinsaid bottom (101) comprises a permanent magnet and said cursor (30)comprises a ferromagnetic element.
 5. Electro-actuator (1) according toclaim 1, wherein said bottom (101) comprises a permanent magnet and saidcursor (30) comprises a permanent magnet.
 6. Electro-actuator (1)according to claim 1, where for the opening of the outlet channel (22),that is for the switching on of the burner, through a manual orautomatic action, the ferromagnetic element (32) of the stem (21) withthe safety electromagnet (4) are brought into contact and kept integralat least until the activation of said safety electromagnet (4)subsequent to the switching on of the burner.
 7. Electro-actuator (1)according to claim 1, where for the opening or the voluntary closure ofthe outlet channel (22), that is for the voluntary switching on and offof the burner, the user manually couples and uncouples saidferromagnetic element (32) of said stem (21) with said electromagnet (4)through said actuation means.
 8. Electro-actuator (1) according to claim1, further comprising at least a solenoid means (33) cooperating withsaid cursor (30) through a suitable magnetic field, so as to achieve theopening or the voluntary closure of the outlet channel (22), that is thevoluntary switching on or switching off of the burner, throughelectrical supply to said solenoid (33).
 9. Electro-actuator (1)according to claim 8, wherein said command force (FS) is the resultantof the forces generated by the solenoid (33) acting on said cursor (30),the direction and intensity whereof depend on the sign and intensity ofthe current circulating through the coils of the solenoid (33); saidcommand force (FS) being characterized in that: to command the openingof said outlet channel (22) said command force (FS=FS_MAX(+)) is greaterthan said maximum mutual attraction force (FF=FF_MAX); to command theclosing of said outlet channel (22) the sum of the command force(FS=FS_MAX(−)) and the minimum mutual attraction force (FF=FF_min) isgreater than the maximum anchoring force (FP=FP_MAX). 10.Electro-actuator (1) according to claim 9, where for the opening of theoutlet channel (22), that is for the switching on of the burner, theuser, through said actuating means, activates the electrical supply tosaid solenoid (33), which remains energized at least until theactivation of said electromagnet (4) subsequent to the switching on ofthe burner.
 11. Electro-actuator (1) according to claim 8, wherein saidcursor (30) is a permanent magnet and for the voluntary closure of theoutlet channel (22), that is for the voluntary switching off the user,through said actuating means, activates the electrical supply to thesolenoid (33), reversing the polarity of said solenoid (33) with respectto that provided for the opening of the outlet channel (22), that is forthe switching on of the burner.
 12. Electro-actuator (1) according toclaim 8, wherein said solenoid (33) can be fed with a square wave withduty cycle.
 13. Electro-actuator (1) according to claim 7, wherein saidcursor (30) is a ferromagnetic element and for the voluntary closure ofthe outlet channel (22), that is for the voluntary switching off, theuser, through the actuating means, cuts off the electrical supply to thesafety electromagnet (4).
 14. Electro-actuator (1) according to claim13, wherein said cut-off of the electrical supply to the electromagnet(4) takes place by closing a by-pass circuit of the electromagnet (4).15. Electro-actuator (1) according to claim 13, wherein said cut-off ofthe electrical supply to the electromagnet (4) takes place through anormally closed microswitch on the circuit of the safety electromagnet(4), which the user opens to cut-off the electric current. 16.Electro-actuator (1) according to claim 1, characterised in that itfurther comprises an interference membrane (230) placed in the proximityof said stem (21) inside the said conduit (23) of the fuel gas. 17.Cooktop with blown burners that use the electro-actuator (1) accordingto claim
 1. 18. Electro-actuator (1) according to claim 8, wherein saidcursor (30) is a ferromagnetic element and for the voluntary closure ofthe outlet channel (22), that is for the voluntary switching off, theuser, through the actuating means, cuts off the electrical supply to thesafety electromagnet (4).
 19. Electro-actuator (1) according to claim18, wherein said cut-off of the electrical supply to the electromagnet(4) takes place by closing a by-pass circuit of the electromagnet (4).20. Electro-actuator (1) according to claim 18, wherein said cut-off ofthe electrical supply to the electromagnet (4) takes place through anormally closed microswitch on the circuit of the safety electromagnet(4), which the user opens to cut-off the electric current.